1. Field of the Invention
The present invention relates to a test circuit, and more particularly to a test circuit for analyzing and evaluating a characteristic of an analog signal of a device.
2. Description of the Background Art
In order to test a semiconductor device including a variety of analog circuits, a test circuit capable of evaluating a characteristic of an analog signal output from a semiconductor device in high speed with high precision has been necessary. Examples of a method of testing a system LSI include BIST (Built-In Self-Test) in which a test circuit is embedded within a chip of a system LSI and BOST (Built-Out Self-Test) in which a circuit for testing an analog signal is provided on a load board of an LSI tester.
In order to evaluate the characteristic of the analog signal of the device in high speed with high precision, however, an expensive AD converter has been necessary. In addition, as data should constantly be taken in for obtaining an arbitrary signal waveform, a storage circuit of a large capacity has been necessary.
Japanese Patent Laying-Open No. 05-119064 discloses a waveform measuring device realizing measurement resolution higher than resolution attained by an employed AD converter, by digitizing an analog input signal (repeated signal) by division of a voltage range and by overwriting digitized data on a display unit.
In addition, Japanese Patent Laying-Open No. 2000-292469 discloses a jitter measuring device measuring jitter contained in a periodic signal in real time.
As described above, a conventional test circuit has required an expensive AD converter in order to evaluate the characteristic of the analog signal of the device in high speed with high precision. Moreover, a storage circuit of a large capacity has been necessary for constantly taking in data.